That plug-in is no longer supported, but it works. For those who are curious to use it in the future, copy the directory to your plugins folder, activate it through WordPress Administration, and then go to Options, then go look for CQS at the top.

Go to "New Condition", then choose "is_month" from the drop-down menu. Type in "-1" (no quotes) where it says "show __ per page", and then click Add. Now, whenever someone checks a month on your page, it'll show the entire month's postings.